LONDON (Reuters) - Scientists have found important genetic
differences between people that may help explain why some
smokers get lung cancer and others do not.

Three teams from France, Iceland and the United States said
on Wednesday they had pinpointed a region of the genome
containing genes that can put smokers at even greater risk of
contracting the killer disease.

In all three studies, nicotine appears a major culprit.

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The findings could eventually lead to better ways to
prevent and treat lung cancer, the biggest cause of
cancer-related death globally in men and the second most common
in women.

"It opens the possibility that treatments that block these
genes could be very beneficial as a treatment strategy against
lung cancer, as well as against addiction," Paul Brennan of the
International Agency for Research on Cancer in Lyon, France,
told reporters.

Smoking causes nine out of 10 cases of lung cancer. Yet
only about 15 percent of smokers actually develop the condition
and doctors have long suspected that a genetic element is
involved.

The new research confirms some smokers are indeed more
vulnerable because of their DNA profile. Smokers with two
copies of the genetic variations stand around a 23 percent risk
of lung cancer, according to Brennan.

The findings mark another step in unraveling the genetic
basis of diseases by analyzing common changes in the genetic
code known as single nucleotide polymorphisms, or SNPs
(pronounced "snips).

Since early 2007, variations at nearly 100 places on the
genome have been linked to diabetes, heart disease and certain
cancers.

NICOTINE'S ROLE

Significantly, all three groups publishing results in
Nature and Nature Genetics zeroed in on tell-tale variants in
the same area of chromosome 15 that hosts three nicotine
receptor genes.

That might suggest nicotine itself is carcinogenic as well
as addictive. Alternatively, it could simply be that some
people are more likely to get addicted to cigarettes and smoke
more, thereby exposing their lungs to greater damage.

"We need to get a better handle on how genetic factors
increase risk and what molecular pathways are involved in
development of lung cancer," said Chris Amos at the University
of Texas M.D. Anderson Cancer Center in Houston.

Kari Stefansson, the chief executive of Iceland's Decode
Genetics Inc, whose scientists conducted the third study and
which sells tests to assess risks for other diseases, was
cautious about the value of screening for the new DNA traits.

"This is the first step in understanding what sequence
variants lie behind lung cancer and nicotine addiction," he
said.

Other researchers also warned personalized testing could
weaken the public health message that everyone should quit
smoking. Even if some people have a degree of resistance to
lung cancer, they will still likely be vulnerable to
smoking-related heart disease and serious respiratory
disorders.

Smoking is also the leading cause of heart disease, the
number one killer in the developed world, and emphysema.